Light sources are used in all types of illumination and projection applications. Many applications require an illumination system with a high level of brightness in a small effective emitting area. This high level of brightness can be accomplished conventionally by adding more light sources. However, this can be both technologically impossible if there is a limited space for integrating light sources and economically unfeasible as it can be expensive to integrate and use multiple light sources. Accordingly, the present invention proceeds upon the desirability of increasing the brightness of a light source without increasing the number of the light source.
For example, micro-display based television (MDTV) has the potential of being low cost with large screen size. Traditional MDTVs are usually illuminated by arc lamps. Although this light source is the brightest at the lowest cost, the need to split the white light into 3 colors and the short lifetime make is less desirable. With advances in LED technology, the use of LED as the light source in MDTVs has to be considered to capture the long life feature of LEDs and other benefits such as instant ON. However, at the present time, LEDs are not bright enough for low cost application using small imaging panels or with larger screens. LED recycling scheme has been used to enhance the brightness of the light source, see U.S. Pat. No. 6,869,206 issued to Zimmerman et al. However, Zimmerman et al. describes enclosing the LEDs in a light-reflecting cavity with one light output aperture. Also, U.S. Pat. No. 6,144,536 issued to Zimmerman et al. describes a fluorescent lamp having a glass envelope with a phosphor coating enclosing a gas filled hollow interior. A portion of the light generated by the phosphor coating is recycled back to the phosphor coating. The claimed invention proceeds upon the desirability of providing higher brightness at the screen through efficient coupling of light from one or more light sources to the output, particularly by increasing the brightness by recycling using light pipes with one or more light sources and incorporating the same in a projector.
For example, LEDs are one type of light source used in many illumination applications such as general lighting, architectural lighting, and more recently in projection televisions. Due to the low brightness of the LEDs, most of the display or projector systems are etendue limited, which generally sets a ceiling to the maximum output at the screen. When used in projectors for example, LEDs must emit light in a small effective emitting area at a high brightness level in order to provide the requisite high light output on the projector screen. Specifically, the LEDs must provide an intense and bright light as measured in lumens at a small and solid angle in a small emitting area to be useful in projectors.
Although there had been tremendous advancement in the light emitting diode (LED) development, the output brightness of currently available LEDs is still not sufficient for most projection applications. Various methods had been proposed used to combine LED's with primary colors and recycling of output light to increase brightness. However, most of them these methods involve utilizing expensive components and/or results in a large, bulky device which greatly limits their applications. Therefore, the claimed invention proceeds upon the desirability of providing system and method for increasing the brightness by recycling using light pipes with one or more light sources (including but not limited to LEDs, arc lamps, UHP lamps, microwave lamps and the like) that solve these problems, and projectors incorporating the same. The projectors of the claimed invention can also multiplex colors to provide both colored pixel displays and time sequential displays.